Thoughts on a Manual/CNC lathe

My next Camsoft project is going to be lathe. I have a 15" LeBlond manual lathe that I would like add some CNC capability to. I also want to completely retain all of its manual capabilites (ie easily switch between manual and CNC mode). I am just now beginning to think about this, and the following questions have come up:

I do not want to change the spindle motor to a servo, so can I put an encoder on the spindle to allow inches per revolution feedrate programming? Would it be hooked into the main encoder on the last axis, even though there aren't going to be any servo connections?

Is it possible to use the LeBlond Z axis feed (no servo) and have the X axis servo react to the current Z location, almost like an electronic tracer?

Assuming the answer above is NO, as I expect it will be, I can see three options for driving the carraige.

(1) putting a servo on the feed rod (disengaging it from the QC box when in CNC mode) and using the carraige spur gear and rack as in manual operation.
(2) putting a servo on the leadscrew and engaging the half-nuts when in CNC mode.
(3) adding a servo driven ballscrew to directly drive the carraige.

Even though I am going to have linear scales, I believe (1) will have too much backlash to be a viable option. There also isn't an easy way to temporarily disconnect the rod from the QC box. (2) would be OK if I don't run in CNC mode much and don't mind the additional wear on the nuts and leadscrew. (3) is probably the best choice, but would require the most work to implement and be cumbersome to change between manual and CNC modes.

Anyone have any thoughts or words of wisdom?

For the spindle it would be easiest to just use a tachometer or sensor pick-up, I am sure I saw someone posted on this site a prox switch picking up a screw head and calculating RPM, and even if they didn't this works well. PS don't be trying any threading with this set up.
For the Z axis use the ball screw and forget about the manual wheel, put an encoder wheel in its place and digitally run the z axis.
I guess this may not be usefull to you as you will definatly lose your threading ability, but seems the easiest to me.

IMHO, you're going to mess up a nice manual lathe. A good manual lathe is needed in any shop. It would be far easier to find a CNC lathe with a dead control and put camsoft on it.

That said, it would certainly be possible. Replace the X and Z axis with ball screws mounts and servos. For the spindle, you can use the existing drive. Add an encoder with a index pulse to read position and use the last axis on the gail board to read it (three axis board).

Karl

use a encoder on the spindle that will give you thearding and use ball screws or you will get shutdown when it pulls out of position i have done a lot of retro fitting anilams and fanucs on lathes small hardings to 120 inch dia. morando